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Tuesday, July 26, 2011

Troubleshooting: Power-On-Self-Test Failures

Over the years, many customers have come to us after assembling their new computers and finding that their system will just not start up. Here are some things to double-check that we have found wrong before:

  • Did you read the motherboard manual or Quick Start guide?

  • Is the 115/230 Volt switch on the back of the power supply set to 115 Volts?

  • Is the system getting power?

    • Do the fans start to spin when you press the power button?

    • Is there a power-indicator on the motherboard that lights up as soon as the power supply is connected and the power supply switch is turned on?

  • Are all of the power supply plugs inserted into the motherboard? -- even that square one next to the processor socket?

  • Does your video card require additional power connections?

  • Is the RAM properly seated? If you are only using some of the available slots, are the modules in the same bank / channel?

  • Is it the correct speed RAM?

  • Is the heat sink firmly attached? (Many no-start or lockup problems have been found due to this error.)

    • Has heat sink compound been properly applied? (Stock heat sinks usually have phase-change compound pre-applied to the base. Many after-market heat sinks include a tube, bottle, or squeeze-packet of thermal compound. If no compound was applied, the CPU will overheat, even with the cooler correctly mounted.)

    • If your heat sink came with a protective film over the compound, did you remove it before installing?

    • If you have an after-market heat sink, is it seated squarely on the processor? Make sure it clears any system board components, connectors,
      or other obstacles that may be located near the CPU socket. If it has more than one or two lock-down points, make sure all are securely fastened down.

    • Intel stock coolers have lock-down pins that rotate 1/4 turn counterclockwise to release. These should be in the clockwise (locked) position.

  • If you are using a separate video card with a motherboard that already has  integrated video -- is your monitor attached to the correct video connector?
    (The video card in the expansion slot should disable on board video automatically.
    If you don't see the POST screen or graphical splash screen at power-on, you can check this by attaching the video to the onboard connector. To test the base hardware, pull the video card and test with just the onboard video connected.)

  • Did you double-check the front panel switch connections to make sure that they attach to the correct pins on the motherboard?

  • If you have a reset switch, try removing this connection at the motherboard if there are separate connectors. Check for stuck reset or power buttons on the front of the case.

  • Did you skip installing the standoffs and screw the motherboard directly
    to the chassis pan? (Don’t laugh; it’s been done more than once.)

  • Try disconnecting any drives, USB, or other devices not specifically required for basic power on testing. You don't need to boot to a hard drive or optical disk, and USB devices may appear to be bootable media to the system. Once you have a successful boot with minimum hardware, then connect additional devices one at a time until you identify which one caused the POST failure.

  • Are you getting any beeps? How many and what kind? Check your motherboard manual.

Only after thoroughly investigating these issues should you start suspecting one or more bad components.

Remember - check the obvious things first...
power button 

  • Is it turned on, plugged
    in, and set to the correct line voltage?

power cables

  • Are all power cables

  • Is the heat sink installed correctly and seated flat on the CPU with
    thermal compound?

  • Is memory seated correctly?

Power cables

  • Are the front panel connections on correctly?

  • Try removing the reset button connection if these are separate connections.

user manuals 

  • Check your user manual for troubleshooting tips.

  • Verify that the components
    like memory and CPU are compatible.

  • Look for a table of POST beep codes if you get startup error signals.

The following table shows some of the more common beep code sequences generated by certain BIOS manufacturers. This is not all-inclusive, and may be different from your specific system board version or manufacturer - check your documentation to be sure.

Award / Phoenix BIOS beep codes:
One short beep when displaying logoNo errors during POST
(This is normal!)
Long beeps in an endless loopNo DRAM installed, DRAM
not detected, or base 64MB memory bad
One long beep followed by three
short beeps
Video card not found
or video memory bad. (Note: Some video cards can generate this code if the
monitor is not attached and/or turned on.)
High frequency beeps when system
is working
CPU overheated. System
running at a lower frequency.

Intel desktop beep codes:
1 beepNo errors - normal startup
2 beeps (beep, beep, <pause>...)No video detected (add-in
card) or unsupported CPU
3 beeps (beep, beep, beep, <pause>...)Memory error
High/Low beeps (warble)CPU overheat or no CPU
fan detected

Intel server board (SE7505VB2) beep codes:
Beep sequence:Meaning
4, 3, 1, 2 beepsNo memory modules detected
4, 3, 1, 3 beepsMismatched memory installed
(usually size of RAM modules, but can also be single-side vs. double side
or configuration of RAM chip access)
4, 3, 1, 4 beepsPaired memory required,
not found. Check to make sure pairs of modules are installed in the same
bank or channel.
4, 3, 3, 1 beepsMemory error - row address
4, 3, 3, 2 beepsMemory error - Internal
4, 3, 3, 3 beepsMemory error - Timing
4, 3, 3, 4 beepsMemory error - Registered
4, 3, 4, 1 beepsMemory error - Registered
/ NonRegistered mix
4, 3, 4, 2 beepsMemory error - CAS Latency
not supported
4, 3, 4, 3 beepsMemory error - memory
size not supported
1, 3, 4, 3 beepsMemory error - base
4 MB

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